4. Discussion
Our data indicate that the Matuyama-Brunhes transition boundary constitutes 5.7 cm, between 7.1-12.8 cm depth of the sampled sedimentary section, of the Za Hajovnou cave sediment. The magnetic reversal is characterized and represented by frequent fluctuations of inclination angle (Fig. 6a) and VGP latitude (Fig. 7a). We think that oscillations in declination data show instability of the Earth’s magnetic field. On the other hand, similar fluctuations which are seen in the previous studies (Fig. 6) show the reliability of the data.
Although the data in this study and Okada et al. (2017) belong to geographically different locations and sediment types, the similarity during polar migration (Fig. 8) shows that the reversal was a dipole transition, and the non-dipole field component was less significant (Oda et al., 2000; Mochizuki et al., 2011; Simon et al., 2019).
In most of the samples with demagnetization generally at 20 mT, some large fluctuations in the data may be considered as instability of remanent magnetization. Although some samples (01_8M, 04_2M, 17_2M, 17_9M, 22_0M) are not demagnetized up to 100 mT, it shows that minerals with low coercivity are responsible for the magnetization of the cave sediments in our study. It can be clearly seen in the rock magnetism measurements that the samples show similar behaviour during the measurements that is maghemite in this case.
Note that most of the section contains samples from the polarity transition. The data shows that the magnetic field was unstable for our oldest sample already, when in reversed polarity. This observation goes well with Yamazaki and Oda (2001) where they show the magnetic pole was unstable long time before the actual reversal boundary and the magnetic field started to fluctuate almost 150 cm deeper than the actual transition (Fig. 7b, 10). We think that our data illustrate the same instability, and this is why no paleomagnetic samples have VGP latitudes that deviate less than 25° from the reversed position. We provide a more detailed explanation of the reversed VGP behavior in our data that show reversed polarity unrest well before the actual magnetic reversal.